Referring to FIG. 1, a sheet cutting device of this type includes a stationary blade unit 10 and a movable blade unit 20 which are opposed to each other across front and back surfaces of a sheet S that has been subjected to printing in a sheet passage inside a printer.
The stationary blade unit 10 includes a frame 11, a stationary blade 12 supported by the frame 11, and a plate spring 13 for pressurizing the stationary blade 12 in a direction toward the movable blade.
The movable blade unit 20 includes a frame 21, a movable blade 72 supported so as to be movable in a vertical direction of FIG. 1 inside the frame 21, a rack 23 fixed to the movable blade, and a pinion gear 24 connected to a drive source (not shown), for driving the rack in the vertical direction of FIG. 1.
This cutting device operates as follows. The sheet S conveyed from the right to left of FIG. 1 is temporarily stopped, and when the pinion gear 24 of the movable blade unit 20 is rotated in the J direction of FIG. 1 by driving a stepper motor and the like (not shown), the movable blade 72 fixed to the rack 23 which meshes with the pinion gear 24 moves (ascends) in the K direction of FIG. 1. The stationary blade 12 and the movable blade 72 are provided in a press-contact state to each other. The sheet S is cut by the principle of scissors, and the cut sheet is discharged from a discharge port of the printer.
By the way, the movable blade 72 includes, at a movable blade leading edge part which engages with the stationary blade 12, a blade edge portion 72a that is thinned toward the movable blade leading edge.
Such a blade edge portion is formed as follows. First, the outer shape of the movable blade is formed by punching. Subsequently, a tool for cutting or grinding, which is a type of a rotation-type file, is obliquely pressed against an end surface of a punched metal plate material, which corresponds to the movable blade leading edge, and cutting or grinding is performed. With this, the blade edge portion 72a as illustrated in FIGS. 2A and 2B is formed.
Besides the movable blade illustrated in FIGS. 2A and 2B, the movable blade including the blade edge portion formed by cutting or grinding is also disclosed in, for example, Related Art Document 1 (Japanese Unexamined Patent Application Publication (JP-A) No. 2003-225887) and Related Art Document 2 (Japanese Unexamined Patent Application Publication (JP-A) No. Hei 10-217182). In the technology disclosed in Related Art Document 1, a blade edge portion called a V-shaped blade portion is formed by grinding. Further, it is also found in the technology disclosed in Related Art Document 2 that, although not clearly described, the blade edge portion is formed by grinding.
However, the type of the rotation-type file to be used in cutting or grinding has a pinpoint and narrow work range. Therefore, the cutting or the grinding is performed by gradually moving such a tool in a width direction of the blade edge portion, which requires a long period of work time and reduces the productivity.
Further, the movable blade generally includes a pair of guide portions for guiding the engagement with the stationary blade at the time of cutting. However, as illustrated in FIG. 2C, the tool for cutting or grinding cannot be pressed against a root part of each guide portion 72c, and hence the blade edge portion 72a cannot be formed to a maximum extent in the width direction of the movable blade. In this case, the roots of the guide portions are thicker than the blade edge portion, and hence, at the time of cutting, the roots of the guide portions may hit the stationary blade more strongly than the blade edge portion, which causes this portion of the stationary blade to be worn greater than the other part (uneven wear). Thus, there is a risk that the durability of the stationary blade is impaired.
Further, as illustrated in FIG. 2B, the tool for cutting or grinding cannot be pressed against the inner side of a non-cutting portion 72b for performing partial cutting of a sheet as well, and hence the blade edge portion cannot be formed in the non-cutting portion 72b. Note that, the non-cutting portion 72b does not cut the sheet at the time of partial cutting, but by controlling the movable blade 72 to increase its stroke, the sheet is completely cut in some cases. Therefore, it is desired that the blade edge portion be formed also in the non-cutting portion 72b. 